"As the Islamic State, also known as ISIS and ISIL, continues to hold large parts of Iraq and Syria and inspire terrorist attacks in more and more countries, it has come to rely upon U.S. social-media companies to summon fresh recruits to its cause," writes The Washington Post , "raising difficult questions for many U.S. firms: how to preserve global platforms that offer forums for expression while preventing groups such as the Islamic State from exploiting those free-speech principles to advance their terrorist campaign."

"In Europe, some governments are requiring social-media companies to block or remove terror-related posts. Earlier this month, the Senate Intelligence Committee approved a bill that would require social-media companies to alert federal authorities when they become aware of terrorist-related content on their sites... Putting more pressure on the social-media companies, a U.N. panel last month called on the firms to respond to accusations that their sites are being exploited by the Islamic State and other groups."

"Facebook has been the most aggressive of the large social-media companies when it comes to taking down terror-­related content. The company has adopted a zero tolerance policy and, unlike other social-media companies, proactively removes posts related to terrorist organizations. Facebook also relies on its users to alert the company to posts that promote or celebrate terrorism and hires screeners to review content that might violate its standards."

"Another challenge for the companies: It is often difficult to distinguish between communiques from terrorist groups and posts by news organizations and legitimate users. Internet freedom advocates also note that much of what groups such as the Islamic State are posting can be seen as part of the historical record — even though many of the photographs and videos are horrific."